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Power being used when computer is off

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  • Power being used when computer is off

    I'm not sure if this is a good idea or not, but I was thinking of leaving the computer on "soft off" (ATX off feature that allows it to turn on using button, time, etc.). I know that the ATX spec. says something about taking up about 750 mA when off, however I don't know if this is how much it is actually taking, or if it just needs this amount of power available.
    Anyone have any experience with leaving a computer plugged into the battery on soft off, and if so, were they good experiences? Does the computer take enough power when off to drain the battery, or would it take forever and a day?

  • #2
    Well Let me say a few things. First, from what I believe soft-off is when we click the shut down and the computer goes off from there, meaning that it will not stop at the "turn off computer now" screen. This does not effect the start-up or anything else. So yes you can use it. Now ATX mobos draw power always, even when off, so if your using an inverter than you cut the power from there and you will not have a drain from the ATX board, but the drain is so small that it will not effect your cars operation. 750 milli amps off the 3.3 volt line, ( i am almost sure of that, someone correct me if they know better) is what the mobo will require when off, if using DC-DC,(with a direct line of power) and thats only because the ATX listens for the switch which is plugged into the board, and the board turns on the power supply. That holds true with or with out soft-off. Soft-off is just a feature.
    Mine stays on all the time. If I am going somewhere, and stop to get gas, no porblems, or a drink, still no problems.

    Have fun,
    Subject open, Subject closed.


    • #3
      It really depends on the motherboard. Some of the newer ones provide power to the keyboard and network card etc when the computer is off. I have an older atx motherboard that uses around 1 millamp with the computer off. All it uses it for is listening to the power button.

      The best plan is to get a current meter (less than 20 bucks) and measure it.
      MPEGBOX - Plexiglass Computer


      • #4
        If you are going to use soft off, the best idea is to avoid the inverter. It will draw unnecessary amounts of power.

        If you really want to cut down on power requirements, set the jumper on the motherboard that disables "keybaord power on". That feature keeps the keyboard running when the system is off, and takes about 1A.
        Player: Pentium 166MMX, Amptron 598LMR MB w/onboard Sound, Video, LAN, 10.2 Gig Fujitsu Laptop HD, Arise 865 DC-DC Converter, Lexan Case, Custom Software w/Voice Interface, MS Access Based Playlists
        Car: 1986 Mazda RX-7 Turbo (highly modded), 1978 RX-7 Beater (Dead, parting out), 2001 Honda Insight
        "If one more body-kitted, cut-spring-lowered, farty-exhausted Civic revs on me at an intersection, I swear I'm going to get out of my car and cram their ridiculous double-decker aluminium wing firmly up their rump."


        • #5
          When in an "off" state, ATX motherboards draw power from a special 5V line called 5VSB (5 volt stand-by). The ATX spec allows for several hundred mA to be drawn from this line for things like WOL (Wake on LAN), WOR (Wake on ring), etc. Also, on many motherboards the USB bus remains powered with +5V from this as well, even when the PC is "Off".

          This is also used for powering on of the system. When you press the power button (or mouse click, hotkey, or password), the motherboard actually signals the PSU to turn on. In order for this to all work, there has to be a constant power to the motherboard.

          When the PSU is off, all other voltages are at 0 volts, EXCEPT the +5VSB.
          Jason Johnson
          Yorba Linda, California

          MPC Phase IV - *** PENDING ***